Stator construction for axial flow compressor



May 6, 1958 F. w. w. MORLEY 3,

STATOR CONSTRUCTION FOR AXIAL FLOW COMPRESSOR Filed Oct. 25, 1954 2 Sheets-Sheer. 1

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STATOR CONSTRUCTION FOR AXIAL FLOW COMPRESSOR Filed Oct. 25, 1954 2 Sheets-Sheet 2 v I/VVEA/ToR Fri/50 mm ww. MORL Y QIEMEYS United States Patent STATOR CONSTRUCTION FOR AXIAL FLOW COMPRESSOR Frederick William Walton Morley, Castle Donington,

England, assignor to Rolls-Royce Limited, Derby, England, a British company Application October 25, 1954, Serial No. 464,511

Claims priority, application Great Britain November 6, 19 53 1 Claim. (Cl. 230-133) This invention relates to axial-flow compressors and is more particularly concerned with stators for multi-stage axial-flow compressors having a casing made in a number of part-annular sections and a row of blade elements for each of a number of compressor stages mounted within the casing. Usually, in such a stator construction, the casing is made in halves joined along abutting, axially-extending edges.

In thespecification of U. S. Patent No. 2,543,355 (Davis et al., assignors to Rolls-Royce Limited), there is described such a stator structure comprising a casing having a relatively thin wall provided internally with reinforcing webs extending circumferentially around the wall and projecting radially inwards therefrom, which webs are formed with surfaces adapted by being curved about the axis of the casing to serve in use to retain circumferentially assembled stator blades radially in position with respect to the wall of the casing in a manner to provide a space or clearance between the blade roots and the wall, and some of which webs are provided with inwardly-facing surfaces curved about the axis of the casing to constitute portions of the outer Wall of the working fluid passage through the compressor casing. The webs comprise main webs having outwardly-facing curved retaining surfaces and of which the inwardly-facing surfaces constitute the outer wall portions, and intermediate webs between the main Webs and having inwardly-facing, curved retaining surfaces. Each blade element has its root formed at its axially-spaced edges with inwardlyfacing curved surfaces to co-operate with the outwardlyfacing retaining surfaces in the main webs and formed between said edges with a rib having an outwardlyfacing curved surface to co-operate with the retaining surface of an intermediate web.

Such a construction of stator has the advantages that the external surface may be substantially free from projections and that the blades are properly and readily located. However the retaining surfaces must be accurately machined and the operation of machining the casing internally is a diflicult one.

The present invention has for an object to provide an improved stator construction in which such high accuracy of machining of the casing is not required.

According to the present invention, a stator for an axial-flow compressor comprises a casing with internal reinforcing webs and made in a number of part-annular sections, a row of stator blades for each of a plurality of stages of the compressor, each blade having a root with curved locating surfaces at its axially-spaced edges, and a plurality of blade carrier rings, each ring being adapted to receive one row of stator blades and being formed in a number of arcuate sections corresponding to the casing sections, each ring having formed in its radiallyinner surface a channel with grooves in its side walls, which grooves have locating surfaces curved about the casing axis to be engaged by the locating surfaces of the blade root, whereby the blades are retained in the rings, and each ring being received between a pair of reinforcing webs and having its axially-spaced edges shaped to interlock with the reinforcing webs to be retained radially but free for engagement with the webs by circumferential sliding.

With this arrangement, the interlocking features on the reinforcing Webs of the casing and the rings need not be machined to very close limits, and so the casing machining operations are facilitated. The blade-retaining grooves of the individual blade-carrying rings are on the other hand more readily produced to a close limit. In addition the blade-carrying rings may, if desired, be made of different material from the casing.

According to a feature of this invention, the bladecarrying rings may be provided at their edges with axial flanges which extend to close to the adjacent rings thereby to provide the portions of the wall of the working fluid passage through the compressor casing between the blade roots and to protect the casing from the heated working fluid. With this arrangement, the casing may be made from say a magnesium-base alloy which is light in weight but of comparatively low strength at elevated temperatures, and the rings may be made from say in a1umin-' ium-base alloy of good hot strength properties.

One construction of stator according to the invention will now be described with reference to the accompanying drawings in which Figure l is a view on the endof part of one half of the stator casing with part cut away, and Figure 2 is a perspective view illustrating how the blade carrying rings and blades are connected together into the casing.

The stator comprises a casing of substantially frustoconical form made in two sections 10 each of which is substantially semi-circular and which abut over axiallyextending surfaces and are joined in assembly by bolts which pass through holes in swellings 11 externally of the casing. The casing is formed internally with reinforcing webs 12 each ofwhich is formed on each of its axially-facing surfaces with axially-projecting ribs 13. There is thus formed between each pair of webs 12 a channel 14 With grooves 15 in its side walls. There is such a channel 14 for each stage of stator blades to be mounted in the casing. The sides of the grooves 15 are machined to be curved about the casing axis.

In each channel 14, there is located a blade-carrying ring 16 which is made in halves, one of which is in one section 10 of the casing and the other of which is in the other section 10 of the casing.

Each ring 16 has at its axially-spaced edges axially- .projecting flanges 17 to engage in the grooves 15 with the radially-inner and outer surfaces of the flanges 17 in contact with the sides of the grooves 15 to locate the ring 16 radially.

Each ring 16 also has at its axially-spaced edges radiallyinwardly projecting flanges 18, the axially-facing outer surfaces of which bear against radially-inner ends of the webs 12 to locate the rings axially in the casing. The flanges 18 also form the side walls of a channel 19 on the inner side of the ring 16 and the flanges have accurately machined in them grooves 20 which are circular about the casing axis.

Each ring 16 carries the blades 21 of one stage of the compressor. Each blade 21 has a root platform 22, the axially-spaced edges of which have axial projections 23 whereof the inner and outer surfaces are accurately machined to the same curvature as the grooves 20). Thus when the blades 21 have their roots 22 threaded. into the channel 19 of the appropriate ring 16, the blades are located radially. The axially-facing end surfaces of the roots 22 fit betwen the inner ends of the flanges 18 and so the blades 21 are located axially. The roots 22 of the blades 21 in a ring 16 abut one another circumferentially.

Each ring 16, except those at the end of the casing, has at the inner ends of its radial flanges 18 axial flanges 24 which extend on assembly of the compressor to near to the flanges 24 on the adjacent rings 16. The gap between adjacent flanges 24 is preferably such as to be substantially taken up by relative thermal expansion of the parts under the temperature conditions met in operation. Thus the flanges 24 cover the inner ends of the webs 12 to protect them from being overheated by the hot compressed air in the working fluid passage of the compressor, and the heat transfer to the casing sections 10 is reduced and the casing may therefore be made of a material having a lower hot strength than the material of the rings 16.

In assembling the compressor, the blades 21 are first assembled in the appropriate halves of the rings 16 by threading their roots 22 around the channels 19, and the appropriate half rings are then assembled in each casing section 10 by threading them into the channels 14.

The ring halves and blades are then located circumferentially by washers 25 which are accommodated in recesses 26 in the abutment flanges of the casing halves and which overlap the ends of the ring halves and the roots 22 of the end blades 21. The washers are retained by set screws 28 screwed into hollow bushes 29 secured in the abutment flanges of the casing halves.

It has been found that with the above construction, machining of the casing is facilitated since such a high accuracy is not required, and also since the casing is protected against overheating it may be of a light material such as a magnesium-base alloy, having a low hot strength compared with the material of the rings 16.

Iclaim:

A stator for a multi-stage axial-flow compressor comprising a casing having a number of axially-spaced circumferentially-extending internal reinforcing webs, said casing being made of a light alloy and being made in a plurality of part-annular sections; a row of stator blades for each of a plurality of stages of the compressor, each stator blade having a root at one end, the root having axially-spaced circumferentially-extending edge portions, each edge portion having a pair of radially-spaced oppm sitely-and-radially-facing locating surfaces which are curved about the axis of the compressor; and means supporting the stator blades within the casing comprising a plurality of blade-carrier rings, each ring being associated with and carrying a single row of said stator blades, being formed in a number of arcuate sections corresponding to the number of casing sections, and being made of an alloy having good hot strength properties, each ring further having in its radially-inner surface a circumferential channel having a pair of axially-spaced side walls, each of said side walls having a circumferential groove defining a pair of radially-spaced radially-andoppositely facing locating surfaces curved about the axis of the compressor, the roots of the associated row of stator blades being received in the channel with the radially-spaced locating surfaces of the roots in contact with the radially-spaced locating surfaces of said side walls; each ring being received in the space between a pair of said reinforcing webs and having axially-spaced edge portions, said edge portions of the rings and said pair of webs each having a pair of radially-spaced oppositely-and-radially-facing surfaces curved about the compressor axis, the radially-facing surfaces of edge portions contacting the radially-facing surfaces of the webs to retain the ring radially in position but with freedom for engagement with the webs by circumferential sliding, and each of said blade-carrying rings being provided at its axially-spaced edges with axial flanges which extend to near the axial flanges on the next adjacent bladecarrier rings and provide portions of the wall of the working fluid passage through the compressor between the blade roots.

References Cited in the file of this patent UNITED STATES PATENTS 

